What are the typical output types from a DDC to control HVAC devices?

• A. Analog outputs (0-10 V or 4-20 mA) and digital outputs (on/off relays or SSRs).
• B. Fiber optic outputs.
• C. Network packets.
• D. HDMI outputs.

Answer: (A)

The signals a DDC uses to drive HVAC devices are two main types: analog signals for proportional control and digital signals for discrete on/off action. Analog outputs provide a continuous control value, typically in a range like 0-10 V or 4-20 mA. The 0-10 V option is a voltage signal that many actuators use to position a valve or damper in a proportional way, while a 4-20 mA current loop is favored for longer runs or noisier environments because it carries the same control value as current, which is less susceptible to signal drop over distance.

Digital outputs are used to switch devices on or off, driving relays or solid-state relays (SSRs) to energize fans, pumps, or damper actuators as needed. This covers the discrete actions the system must take, such as starting or stopping equipment.

Other options aren’t typical ways a DDC controls HVAC hardware: fiber optic outputs are mainly about data communication links, not direct actuator control; network packets describe communication data rather than a direct control signal; HDMI is unrelated to HVAC control signals.